Many television receivers include provisions for displaying a secondary image or picture within a main picture. For example, characters and/or graphics may be displayed on the screen of a display device together with a main picture derived from a video signal provided by a tuner. Such "on-screen display" (OSD) provisions are useful for providing status information, such as the channel number of the presently selected channel, the present time and the volume level, and operating instructions for various functions of the receiver. Some television receivers include provision for inserting a small picture (or "insert") within a main (or "big") picture. In such a "picture-in-picture" (PIP) arrangement, the main picture may be derived from a video signal provided by a tuner and the small picture may be derived from an auxiliary video source, such as a second tuner, VCR or video disk player.
The secondary image or picture provided by an OSD or PIP arrangement is synchronized by synchronization signals derived by the deflection section of the television receiver so that it is properly positioned relative to the main picture. However, other timing signals which are necessary for the generation of secondary image or picture and which are derived from the synchronization signals may be improperly shifted in time because of centering adjustment, depending on how the centering adjustment is achieved.
For example, in a PIP arrangement, it is usually necessary to demodulate a composite color video signal corresponding to the small picture and to remodulate it utilizing a color subcarrier signal which is locked in frequency and in phase with the color subcarrier of the color video signal corresponding to the main or big picture so that the two video signals can be combined and processed together in a common signal processing section. Remodulating the video signal corresponding to the small picture involves extracting the color burst component of the video signal corresponding to the main picture and using it to control the frequency and phase of a color oscillator in the PIP processing section. Extracting the color burst requires the generation of a burst gating pulse timed so that it may be utilized to separate ("gate-out") the color burst component from the video signal corresponding to the main picture. If the gating pulse is derived from a sychronization signal derived by the deflection section, its position in time may not be proper relative to the occurrence of color burst component, especially if a certain type of centering adjustment has been made.